Nitrogen Concentration and Nitrogen Mineralization by Nonleguminous cover crops: Applications - PowerPoint Presentation

Nitrogen Concentration and Nitrogen Mineralization by Nonleguminous cover crops: Applications to central Oregon cropping systems Crop and Soil Science Department Joshua Neuman

Overview Presentation focused on lab incubation of nonleguminous cover cropsOriginal intent was to get Nitrogen (N) mineralization from cover crop and subsequent cash crop N uptake data Field experiment failed and its results will not be discussed

Place of Nonleguminous Cover Crops In Central Oregon Central Oregon growers are starting to use nonleguminous late-summer planted cover crops, especially brassicasThese covers provide several agroecosystem services: Erosion control (and weed suppression)Improved soil structure/water infiltrationCrop rotation (reducing pathogen load by breaking monoculture)Biofumigation (from brassicas with high glucosinolate levels)Nitrogen (N) “catch crop”

Brassica vs Small Grain Covers Forage radish (Raphanus sativus) can root to 2.5 m and take up substantial amounts of N N scavenging and resupply in Fall-planted forage radish 162 kg/ha (Thorup-Kristensen 2006) Brassicas are the fastest-growing cover cropsAccumulate up to 8,000 lb/ac. biomass and achieve 80% ground cover (Chen et al., 2012)Fall small grain cover crops retain more N than Fall brassicas if the brassica is planted too late (Voss and van der Putten, 1997)

Brassicas: Nitrogen Suction Pumps Brassicas have relatively low C:N ratios, similar to legumes, on the order of 37-41 g/kg N shoot dry weight (Brennan et al., 2013)This makes decomposition and N release more rapid than any other non-leguminous cover crop Critical N concentration for net N mineralization from cover crop dry matter is generally 14-18 g/kg N Following high residual N crop (e.g. potato) can accumulate and recycle a lot of NReduced fertilizer N cost

30” (76 cm) taproot

Nitrogen Resupply Knowledge Gaps Growers want to know three things about the N dynamics of nonleguminous cover crops:How much N is needed to establish an overwintering nonleguminous cover crop? How much N will the cover crop return to a subsequent spring cash crop?When will that N be released from tillage-incorporated cover crop residues?

Synchrony: the Key to Coordinating N Return to Crops Synchrony: temporal coordination of N mineralization from decomposing cover crop residues with cash crop N needsPrevious research has found brassica N mineralization to reach levels of 75% N release within 5 weeks (Brennan et al., 2013, Vos and Van der Putten, 2001, Weinert et al., 2002)

OREGON STATE UNIVERSITY 8 http://corn.agronomy.wisc.edu/Crops/Wheat/L007.aspxPeriod of N uptake: Feekes 6-10

Hypotheses of Research Project Nitrogen concentration in young mustard, radish, and oat cover crop residues is a function of N fertilization rate. Nitrogen mineralization is a function of N concentration in young mustard, radish, and oat cover crop residues. Nitrogen mineralized at room temperature will be highest at 4 weeks of incubation and by the 8th week, there will be little N release from young mustard, radish, and oat cover crop residues.

Objectives Field experimentObserve the effect of different N rates and cover crop species on yield and protein content of wheat at harvest Laboratory experiment Observe the effect of N rate on cover crop N concentration Observe the effect of N concentration on N mineralization

Materials and Methods: Field Trial Experimental location: Central Oregon Agriculture Research and Extension Center (COAREC)Soil type: Madras Loam Previous crop: Spring wheat

Materials and Methods: treatments 4x cover crop treatment Mustard Forage radish Oats Soil-only control4 x N fertilizer rate 0 kg/ha45 kg/ha90 kg/ha135 kg/ha

Materials and Methods: field setup 4x4 factorialRandomized complete block design (RBD) 4 x replications16 treatments x 4 replications = 64 subplotsPlot size: 16’ wide x 30’ long (4.9 x 9.1 m)4’ (1.2 m) between plots w/in row5’ (1.5 m) between rep rows

Materials and Methods: field trial Variables measured Soil NO3- N and NH4- N to 15 cmMeasurement intervals: Pre-cover crop planting for background NPost-cover crop for residual N not taken up/N released from decomposition of dead coversPost-wheat harvest NGrain head NData from field trial will not be shown

Materials and Methods: lab incubation Cover crops grown in seeding trays in greenhouse Grown 10 weeks Fertilizer rates were identical to field but scaled to 0.2 m2 tray Plants harvested, cut at soil level and washed of soil then frozen until use in incubation experiment

Materials and Methods: lab incubation Each cover crop species sample oven dried and analyzed for total N content 2 g of cover crop residue oven dried at 60oC for 72 hrOven dried residue ground in plant mill 150 mg of each sample was combusted in Elementar and analyzed for total N

Materials and Methods: lab incubation Cover crop residues aerobically incubated in plastic bags with field soil to determine mineralization rate Residues chopped into 15 mm pieces for rapid decomposition Water added on weekly basis to achieve original gravimetric water content of each bag at beginning of experiment8 week incubation

N fertilizer rate Mustard OatRadishKg/ha% N02.542.412.24453.293.033.0790 3.673.663.40 135 3.81 4.24 3.90 Mean tissue N concentration as function of N fertilizer rate after 8 weeks of growth in a greenhouse setting for aboveground biomass. Plants were grown in a Madras loam soil. Four replications in a non-randomized design. Results

Mean tissue N concentration as function of N fertilizer rate after 10 weeks of growth in a greenhouse setting for aboveground biomass. Plants were grown in a Madras loam soil. Four replications in a non-randomized design.

Week 4 Week 8 NO3-N concentration in soil-only incubation bags at 4 and 8 weeks. Error bars are standard error of mean (n=4). Madras loam soil.

Week 4 Week 8 NO3-N concentration in soil-only incubation bags at 4 and 8 weeks. Error bars are standard error of mean (n=4). Madras loam soil.

Week 4 Week 8 NO3-N concentration in soil-only incubation bags at 4 and 8 weeks. Error bars are standard error of mean (n=4). Madras loam soil.

Discussion NO 3-N mineralization over the 8-week period ranged from 46-245 kg ha-1 for all cover crops %N levels ~4% to release large amounts of N (Sullivan, not yet published)Need either residual soil N or fertilizer rates of 90 or 135 kg ha-1 to get these concentrations based on results of experimentAt phenological stage of small grain termination in this experiment, not a lot of N return1 ton ac-1 dry matter at pre-jointing vs. 10 ton ac-1 at maturity12 lb ac-1 N vs. 120 lb ac-1 N at pre-jointing vs. at maturity

Conclusion Increasing N fertilizer rates increased % N in cover crop residues 90 and 135 kg N ha-1 fertilizer rates produced cover crops with the highest % N and greatest N mineralizationSimilar levels of mineralization seen at 4 and 8 weeksTwo-month N mineralization window extends availability of cover crop N to subsequent cash crop

Acknowledgments My committee: Markus Kleber, Amber Moore (Crop and Soil Science) and Chris Mundt (Botany and Plant Pathology) for providing editorial advice Russ Karrow, administrator of the Agricultural Research Fund, for providing the funding for this project Clara Weidman and Eliza Smith for helping me with graphs and tables and formatting of Masters Project Report